This invention relates to the field of hot dip molding and specifically relates to a dip mold having an internal air vent to allow plastisol to form a full internal part on the molded object. The invention also relates to a dip molding process in which an internal part is formed while air trapped in the mold is released through the mold.
Conventionally, when using a hot dipping process, a heated mandrel is dipped into a plastisol so that the heat from the mandrel causes the surrounding plastisol to jel on the mandrel. The mandrel is then withdrawn from the plastisol at a slow steady rate to prevent runs and drips. The mandrel with the jelled plastisol thereon is then post-baked in a forced air oven or in a bath of molten salt or other non-compatible oils to cure the plastisol. After a predetermined time the mandrel is taken out of the post-bake medium and either air cooled or water cooled after which the plastisol part is stripped from the mandrel.
When the part to be molded has an internal part so that the plastisol must move into an external cavity to form the internal part, there is air in the cavity which resists the movement of the plastisol into the cavity. As plastisol moves into the cavity the air tends to be compressed, thus increasing resistance to flow of plastisol into said cavity.
I have found that by forming a small lateral passage from the depths of the cavity through the side wall of the mold, the air will escape into the passage and allow a full internal part to be formed on the molded item. The size of the passage is small enough that the plastisol does not enter it, so that the outer wall of the molded internal part is smooth.
Accordingly, it is a principal object of this invention to provide a dip mold and process in which an object is molded with a complete internal part.
It is another important object to provide a dip molding process in which the dip mold has an internal cavity on its outer end to form an internal molded part on the object to be molded, and the dip mold is provided with a lateral passage connecting the innermost part of the internal cavity with the outer side wall of the mold to allow air to escape from the cavity.
These and other objects and advantages will become apparent hereinafter.